Examples of cleaning and degreasing methods which have been applied to metals, ceramics, plastics, and other materials in the past can include alkali cleaning, cleaning with a surface active agent, cleaning with chloro-solvent, and/or cleaning with a fluoro-solvent. Alkali cleaning is cleaning achieved by dipping the material into a warm aqueous or alcohol solution of sodium hydroxide or other alkali agent, or by spraying such a solution. Similarly, cleaning with a surface active agent can be achieved by dipping the material into a warm aqueous solution of a surface active agent, or by spraying such a solution. Cleaning with chloro-solvent involves dipping or vapor cleaning with a chloro-solvent, such as, for example, 1,1,1-trichloroethane, trichloroethylene, and/or perchloroethylene. Finally, cleaning with a fluoro-solvent involves dipping or vapor cleaning with, for example, Freon 113.
Currently, organic solvents used in cleaning processes for various materials include hydrocarbons, halogenated hydrocarbons, propylene glycol ethers, ethylene glycol ethers, esters, or mixtures thereof. These solvents are useful since they can be recycled within the process by distillation. However, the solvents listed also show a very low polarity compared to water. As a consequence, solubility and cleanability of very polar soils is limited. In order to clean the polar soils, cleaning processes have incorporated a separate aqueous cleaning step.